The invention discloses an Al-Mg-Si aluminum alloy and an extrusion method for a sectional bar of the Al-Mg-Si aluminum alloy. The Al-Mg-Si aluminum alloy comprises, by weight percent, 0.9%-1.25% of Mg, 0.5%-0.9% of Si, 0.2%-0.42% of Cu, smaller than or equal to 0.6% of Fe and 0.07%-0.35% of Cr and further comprises one or more elements of smaller than or equal to 0.15% of Mn, smaller than or equal to 0.22% of Zn, smaller than or equal to 0.15% of Ti, smaller than or equal to 0.05% of V, smaller than or equal to 0.5% of Hf, smaller than or equal to 0.25% of Sc, smaller than or equal to 1.0% of Ag and the balance Al. The aluminum alloy with the high mechanical performance is obtained by optimizing alloy components, the content of the alloy components and the sectional bar extrusion technology, and the production efficiency is effectively improved. The problems that in the prior art, conventional aluminum for transportation is low in strength and poor in ductility, the control range of the sectional bar extrusion technology link is wide, stability is poor, online quenching control difficulty is large, quenching uniformity is poor, and the production efficiency is low are solved.